Cephalopoda (Cuvier). Part 7

(1541). The alimentary canal presents the same general structure in all the Cephalopod families. The oesophagus (fig. 287, a, d; fig. 289, s), derived from the posterior part of the fleshy mass of the mouth, passes through a ring formed in the cranial cartilage; or else, as in Nautilus, is partially embraced by processes derived therefrom. It soon dilates into a capacious crop (fig. 289, t), the walls of which are glandular; and being lined with a mucous membrane that is gathered into longitudinal plicae, this organ readily admits of considerable dilatation.

(1542). From the crop, a short passage (fig. 289, u) leads into a strong muscular gizzard (v) resembling that of a granivorous bird, and lined in the same manner by a thick coriaceous cuticular layer: in this gizzard, therefore, the food is gradually bruised and reduced to a pulta-ceous magma.

(1543). At a little distance from the gizzard there is, in the Nautilus, appended to the side of the intestine, a globular viscus (y), which is hollow, and its cavity communicates freely with the intestinal canal. The interior of this organ Professor Owen found to be occupied by broad parallel laminae, puckered transversely, so as to offer a great extent of surface; and when examined under a lens, their structure was seen to be follicular, and evidently fitted for secretion. The bile is poured into this cavity, at the extremity furthest from the intestine, by a duct large enough to admit a common probe.

(1544). In other genera this laminated viscus is represented by a caecal appendage to the intestine, placed precisely in the same situation; and on opening it, its internal surface is found to be increased by a spiral lamella that winds closely upon itself from one end to the other. In such cases it is near the apex of the spire that the bile is received from the liver; so that in all essential particulars this spiriform viscus is precisely analogous to the laminated cavity of the Nautilus. There can be little doubt that this apparatus represents a capacious duodenum, and that it is by the extensive surface afforded in its interior that the nutritious portions of the food are separated, as neither the gizzard nor the intestine itself presents an organization adapted to such a purpose. With respect to its other uses Professor Owen remarks that its reception of the biliary secretion renders it in some measure analogous to a gall-bladder; but most probably its chief office is to pour into the commencement of the intestinal canal a fluid which is necessary for the completion of digestion; so that, like the pyloric appendages of fishes, it might be considered to be the representative of a pancreas.

(1545). The remainder of the intestine is a simple tube, which, after one or two turns upon itself, mounts up to the base of the funnel, into which it opens, and thus allows the excrement to be ejected to a distance from the body.

(1546). The liver (fig. 289, z) is of very great bulk when compared with the rest of the digestive apparatus. In Nautilus it is divided into four distinct lobes, which are themselves made up of numerous lobules of an angular form, each being invested with a very delicate capsule. On removing the capsule every lobule is seen to be composed of numerous acini, which with a needle may be readily separated into clusters connected by the ramifications of their excretory duct. In other genera, such as Octopus, wherein these acini have been minutely examined, they have proved to be delicate cells or secerning caeca wherein the bile is elaborated. The excretory canals derived from all the lobules of the liver unite by repeated anastomoses, and thus form two main trunks, which ultimately join, and pour the biliary secretion into the laminated or pancreatic cavity (y).

(1547). In the Cephalopods, as in all the Mollusca, the bile is separated from arterial blood supplied by large vessels derived immediately from the aorta, - no system of veins analogous to the vena portae of higher animals being as yet developed.

(1548). In the Dibranchiate genera the liver is either undivided, or presents only two lobes; but in other respects its composition and minute structure is similar to that of the Nautilus.

(1549). In all the Cephalopoda, with the exception of the Nautilus Pompilius, there is an orifice in the immediate vicinity of the anus, through which a coloured secretion, generally of a deep-brown or intense-black colour, can be poured in astonishing abundance; and this becoming rapidly diffused through the surrounding water, a means of defence is thus provided; for no sooner does danger threaten, or a foe appear in the vicinity of the Cuttle-fish, than this ink is copiously ejected, and the element around rendered so opake and cloudy, that the Cephalopod remains completely concealed from its pursuer, and not un-frequently ensures its escape by this simple artifice. The organ wherein the inky secretion is elaborated is a capacious pouch, variously situated in different genera. In Octopus it is enclosed in the mass of the liver; in Loligo it is located in the immediate vicinity of the anus; and in Sepia (fig. 290, q) the ink-bag is lodged near the bottom of the visceral sac. On opening it, and carefully washing away by copious ablution the ink within, the cavity of the ink-bag is seen to be filled up with a spongy cellulosity, wherein the blacking material had been entangled; and from this cellular chamber a duct leads to the outward orifice, through which the dark secretion is ejected at the will of the animal, and squirted from the extremity of the funnel.